1. Field of the Invention
The present invention relates, in general, to an apparatus for preventing a battery from overcharging and, more particularly, to an apparatus for preventing a battery from becoming overcharged before the battery fails and for preventing a battery from being subjected to heavier damage when swelling occurs in a battery module due to overcharging.
2. Description of the Related Art
Recently, secondary cells that can be charged and discharged have become widely used as an energy source for wireless mobile devices. In addition, secondary cells have also gained attention as a power source for electric vehicles (EV), hybrid vehicles (HV), and the like, which are regarded as one approach to solving the air pollution caused by gasoline vehicles, diesel vehicles, and the like of the related art that use fossil fuels. While one or two or more battery cells are used for a single device in small mobile devices, a mid- or large-sized battery pack, in which many battery cells functioning as unit cells are electrically connected, is used in mid- or large-sized devices such as automobiles.
Since it is preferred that the mid- or large-sized battery pack be fabricated to be as small and light as possible, small angled cells, pouch type cells, or the like, which can be stacked with a high degree of integration while at the same time having a small weight per capacity, are widely used as battery cells of the mid- or large-sized battery pack. Among these, pouch type cells are especially advantageous, since they are light, have a low possibility of the electrolyte solution leaking, and are inexpensive to fabricate.
Although nickel hydrogen secondary cells have been widely used for these unit cells (i.e. battery cells) of the mid- or large-sized battery pack, development of lithium secondary cells, which provide higher output compared to capacity, have been proposed as a possible alternative. However, lithium secondary cells have low stability. In particular, pouch type cells are strong candidates as the unit cells of mid- or large-sized battery packs, because of the various advantages described above. However, they have low mechanical strength, and leak an inflammable substance (i.e., electrolyte) when a sealant is detached, thereby increasing the risk of a fire. In the mid- or large-sized battery pack, in which multiple unit cells are electrically connected for the purpose of high power and mass capacity, a fire can be extremely dangerous.
Furthermore, in the lithium polymer battery using a pouch, the voltage increases when each cell is overcharged, since an integrated cell is filled with the entire electrolyte. In addition, due to the excessive heat created, the electrolyte inside the cell decomposes to generate inflammable gas inside the cell, thereby causing swelling, i.e. expansion of the pouch. Moreover, a membrane between a cathode and an anode may melt causing a short circuit between the cathode and the anode, thereby causing a fire. Thus, the safety of the vehicle cannot be ensured.
In consideration of such problems, the technique was introduced to prevent overcharging by cutting off power from a battery by deforming a cover of a battery cell when the battery cell swells in response to the battery being overcharged, as shown in FIG. 1. Although this approach may prevent the overcharging, terminal parts are broken in the process, thereby rendering an expensive battery pack useless. Furthermore, toxic gas that occurs during the swelling may threaten the safety of consumers.